My sources (bibliography)
1. Investigating science and technology. Canada: Pearson Education Canada, 2008.
2. Notes written in class
3. Review package

PICTURES
Tweezers:
http://www.bbc.co.uk/schools/gcsebitesize/design/systemscontrol/mechanismsrev2.shtml

Crowbar:
http://www.teachengineering.org/view_lesson.php?url=collection/cub_/lessons/cub_simple/cub_simple_lesson01.xml

Wheelbarrow:
http://www.bbc.co.uk/schools/gcsebitesize/design/systemscontrol/mechanismsrev1.shtml